Re: [Xen-devel] Multiple priviliged domains

[Jan Kundrát <jan.kundrat@xxxxxx>]

Ian Pratt wrote:
> > 3. I don't seem to be able to create more than 8 VBDs. [I am using 
> > xen-2.0.1-src.tgz.]  While trying to start 5 domains, each of which had 
> > two "scsi" disks (/ and swap), I discovered that the 5th domain wouldn't 
> > start until I removed the swap disks from both the 4th and 5th domains' 
> > configuration files -- i.e., not exceeding 8 VBDs total.  A cursory search 
> > through the code didn't reveal any relevant #define's, and I didn't see 
> > anything about this in the Xen docs, so before I look further I thought 
> > I'd ask the list if this is a known limit.  (If so, I am surprised the VBD 
> > structures aren't allocated dynamically to prevent this?)  A search of the 
> > mailing list revealed a message from Ian on 2004-03-10 stating "Mark wrote 
> > a pretty good readme on VBDs and put it in the tree", but I couldn't find 
> > the readme; is it still part of the tree?
>
> Are you using loop files? If so, Linux has a statically compiled
> allocation, set to 8 by default. Fixing this and submitting the
> patch to lkml would a good thing...
>
> I don't believe the VBD code has any such limitations. (We tend
> to use LVM rather than loop files).
If you use files as backend for VBDs in domain0, you use loop device. If 
the CONFIG_BLK_DEV_LOOP in dom0 kernel is compiled as module, you can 
use max_loop parameter while doing modprobe/insmod. And if it's compiled 
directly into the kernel, use max_loop=n boot option.
jkt


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